Using Subqueries to Select Records

Written by Bill Graziano on 17 August 2000

John writes "Okay, here's my problem. I have these two tables: INVOICE, which includes everything about a particular invoice including a vendor_id. The second table is VENDOR, which includes the vendor name for each vendor_id. What I want to be able to do is select from the VENDOR table a list of all of the vendor_names that have appeared in the INVOICE table (even if they have appeared in the INVOICE table many times, I just want them to show up once). Is this possible?"

You could easily use this in your client to dynamically build SQL statements. Your IN clause can also include a SELECT statement which is what we did in our first example. Basically we're having SQL Server dynamcially generate our list of VendorID's based on the SELECT statement in the subquery. The DISTINCT clause isn't technically needed in this case. It makes the code more readable to me. I can easily see the intent of the statement.

You could easily put a where clause on the SELECT in the subquery to restrict the rows even further. Now if you have your heart set on a join, you can create a statement that looks like this: